In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of a Device to Device (D2D) proximity service is discussed as a new function in Release 12 and later (see Non Patent Literature 1).
The D2D proximity service (D2D ProSe) is a service enabling direct communication without passing through a network within a synchronization cluster including a plurality of synchronized user terminals. The D2D proximity service includes a discovery process (Discovery) in which a proximal terminal is discovered and a communication process (Communication) in which direct communication is performed.